Field of the Invention
The invention relates to a process for the preparation of 3-halo- and pseudohalo-alkylsilane esters by addition of hydridosilane esters in the presence of catalysts to the double bond of unsaturated aliphatic compounds which contain, as reacting group, the allyl halide or pseudo-halide structural element with a terminal double bond.
3-Chloropropyltrialkoxysilane, Si-methyl-3-chloropropyldialkoxysilane and Si,Si-dimethyl-3-chloropropylalkoxysilane in particular are used as silane coupling agents, for example for glass fibres, in the foundry industry and as fillers for polymers. The 3-halo- or pseudohalo-alkylsilane esters of formula I in particular are important key products for the preparation of, for example, a variety of mercapto-, amino-, methacryloyloxy- and acryloyloxy-functional organosilanes, which have grown in importance over recent years to become a branch of industry in their own right.
Consequently there have already been attempts in various ways to prepare such products. Current industrial production exclusively employs a two-stage procedure in which allyl chloride is hydrosilylated with trichlorosilane or methyldichlorosilane, generally in the presence of platinum-based catalysts, with the respective chloropropylchlorosilane, which is obtained in yields of between 50 and 83%, being subsequently esterified.
These production processes which are currently practiced are highly material- and plant-intensive but, despite their considerable disadvantages, have to be employed given the lack of better alternatives, since the products are urgently required.
For this reason it has already been proposed, to hydrosilylate allyl chloride using trialkoxysilanes. This method employs various platinum catalysts and it is possible to realize product yields from about 20 to 45%. The reproducibility of certain yields, which are indicated as being up to about 70%, is disputed. Belyakova et al, Zh. Obshch. Khim. 44 (106) 1974, No. 11, 2439-2442, report on the detailed investigation of this reaction path employing platinum catalysis. Moreover, they describe the secondary reactions which occur and confirm product yields ranging from about 20 to 45%. In the presence of rhodium catalysts using the methods described in U.S. Pat. Nos. 3,296,291 and 3,564,266, the product yields are again below 40% and are accompanied by considerable secondary reactions. In the presence of high concentrations of specific dimeric iridium-halide-diene complex catalysts, in accordance with U.S. Pat. No. 4,658,050, the yields determined by gas chromatography reach levels of 75%; however, in preparative terms it is only possible to achieve product yields of 55-60%. Further, the by-products described by Belyakova et al occur in large amounts too. A striking additional disadvantage is the need to use such costly noble metal complexes in a high concentration. Leaving aside the cost factor, this also leads to intolerable impurity and waste problems. A need, therefore, continues to exist for a simple method of preparing 3-halo and pseudohalo-alkylsilane esters at improved yields at reasonable cost.